The present invention relates to a blowby gas treatment device which returns blowby gas having leaked out to a crankcase of an internal combustion engine to an intake system, and especially relate to a blowby gas treatment device for an internal combustion engine with a supercharger, which is provided with a supercharger in the intake system.
In a gasoline engine, there is a problem that blowby gas having leaked out to a crankcase causes deterioration of a lubricating oil. Therefore, a blowby gas treatment device which introduces fresh air into the crankcase and which takes the blowby gas out from the crankcase and returns the blowby gas to an intake system has been used.
The blowby gas treatment device conventionally has structures where a fresh gas passage is provided between an upstream side of a throttle valve in an intake system and a cylinder head of the engine body, where a blowby gas passage is provided between a downstream side of the throttle valve in the intake system and a crankcase, and where a flow control valve (that is to say, PCV valve) changing in a valve opening depending on negative pressure in the downstream side of the throttle valve is provided on the blowby gas passage. In this device, as sufficient negative pressure occurs in the intake system in the downstream side of the throttle valve under an usual operating condition other than a high load region, fresh air is introduced into the crankcase from the fresh air passage through the cylinder head. Furthermore, blowby gas is returned to the intake system in the downstream side of the throttle valve through the blowby gas passage and led to a combustion chamber so as to be pushed out by the fresh air.
Regarding such a conventional blowby gas treatment device, in case of an internal combustion engine provided with a supercharger in an upstream side of a throttle valve of an intake passage, it is impossible to conduct the blowby gas treatment because a downstream of the throttle also has positive pressure in the supercharging region.
Patent Document 1 (WO 2013/021456 A1) discloses a blowby gas treatment device for an internal combustion engine with a supercharger where blowby gas treatment is conducted in a supercharging region. This device includes a bypass passage provided between a downstream side of a throttle valve in an intake passage and an upstream side of a supercharger; and an ejector pump provided in the bypass passage. The ejector pump uses an inspiratory flow returning from the downstream side of the throttle valve to the upstream side of the supercharger as a working fluid. Furthermore, in the device, a top of PCV passage which is connected with a cylinder head cover through a PCV valve is connected with an intake port of the ejector pump. Therefore, a part of intake air is returned from the downstream side of the throttle valve having positive pressure to the upstream side of the supercharger through the bypass passage. Due to this flow, blowby gas is absorbed by the operation of the ejector pump.